In recent years, high-speed, large-volume data transmissions are desired in various user environments such as public, office and home environments and a wireless LAN (Local Area Network) technology is becoming a focus of attention as this data transmission technology. For this wireless LAN, there exist a broadband wireless LAN (e.g. HiperLAN2 or HisWANa, etc.) and a system on which standardization activities are underway in IEEE802.11a or the like.
The broadband wireless LAN is a master-slave type network in which under centralized control by one communication terminal accommodation apparatus, a plurality of communication terminals communicate with the communication terminal accommodation apparatus. More specifically, an access point (AP), which is a communication terminal accommodation apparatus, performs communication-related control over mobile terminals (MT) in a centralized manner. Therefore, an MT is structured to necessarily carry out the communication via an AP when the MT carries out a communication.
Furthermore, HiperLAN2 in particular specifies an inter-terminal communication mode. In the inter-terminal communication mode, a period is given during which terminals can perform direct transmission/reception to/from each other under authorization of the AP. In this case, communications need to be controlled through the AP, but the data itself to be transmitted/received can be transmitted without intermediation of the AP.
On the other hand, centralized control type (Point Coordination Function: PCF) and distributed control type (Distributed Coordination Function: DCF), which are direct connection type networks, are specified as IEEE802.11a systems.
In the case of the centralized control type, a point coordinator (PC) provided with a control function performs communication-related control over a station (STA) in a centralized manner. Therefore, the STA is structured so as to necessarily perform communications under the control of the PC when the STA performs a communication.
On the other hand, the distributed control type is structured so as to perform carrier sensing for a certain time before individual STAs send data and carry out a communication after confirming vacancy in a transmission medium.
In this way, the broadband wireless LAN and IEEE802.11a are standardized as individual wireless LAN systems and attempts are currently being made to merge those systems.
The IEEE802.11a specifies a communication area reservation signal (e.g., NAV: NetworkAllocationVector) and a communication terminal which has received this communication area reservation signal is determined to perform an operation equivalent to that in a case where there is no vacancy in the transmission medium during carrier sensing for a specified period of time.
As described above, when considering merging of a broadband wireless LAN and an IEEE802.11a system, it is expected that the communication area reservation signal (NAV) according to IEEE802.11a is also used for the broadband wireless LAN so as to suppress collision with the IEEE802.11a communication terminal.